Trucks and trailers having a flat load carrying bed are in common usage. The load carried by such vehicles is often a standardized enclosure having a rectangular cross section, irregular shaped objects on a standardized pallet, or pipes positioned on a standardized basket. Numerous other types of load configurations are commonly used.
Trucks and trailers having a flat load carrying bed commonly utilize a rear roller which extends slightly above the vehicle bed and has an axis at right angles to the horizontal direction in which a load is slid onto the vehicle bed. The load extends rearward over the roller at all times and the front of the load rests on the vehicle bed. However, friction between the vehicle bed and the middle and front portions of the load often make it difficult to load and unload the bed. There have been some proposals to reduce friction between the load and the load carrying surface of the vehicle or transportation system. For example, Campos U.S. Pat. No. 2,812,080 is a patent in which an entire bed is raised and lowered to expose and retract rollers which project through openings in the bed. Campos uses very complex apparatus and the lift mechanism would have to bear the weight of the load while transporting the load with the bed raised to have retracted rollers. Langley et al U.S. Pat. No. 3,439,790 is a patent which provides apparatus for lifting a load above a conveyor to prevent damage in transit. Langley uses pneumatic tubes which are inflated and which would tend to deflate during transit if they contained leaks. Achammer U.S. Pat. No. 3,228,542 is a patent in which pivoting links are employed to lift and lower loads relative to rolls, which like Campos necessitates supporting the load weight on the lift mechanism when transporting the load. Seper U.S. Pat. No. 3,549,035 is a patent in which fork lift tines utilize roller bearings on inserts to reduce friction between the tine and a load and a floor but such a device is not practical in a flat bed truck or trailer nor functionally similar to the subject invention.
It is thus an object of this invention to provide a roller bed vehicle in which rollers may be selectively extended through the bed of the vehicle to facilitate loading and unloading and may be retracted so the vehicle bed carries the load weight while transporting the vehicle and to provide a unique roller actuator mechanism array which selectively controls the elevation of rollers under the load.